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    Subject[patch 6/7] sched: use rq->avg_event to resurrect nohz ratelimiting
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    Date

    Entering nohz at high frequency eats cycles, ratelimit it
    just as we do idle_balance(), and for the same reason.

    Signed-off-by: Mike Galbraith <efault@gmx.de>

    ---
    include/linux/sched.h | 2 ++
    kernel/sched/core.c | 7 +++++++
    kernel/time/tick-sched.c | 2 +-
    3 files changed, 10 insertions(+), 1 deletion(-)

    Index: linux-3.0-tip/include/linux/sched.h
    ===================================================================
    --- linux-3.0-tip.orig/include/linux/sched.h
    +++ linux-3.0-tip/include/linux/sched.h
    @@ -1988,8 +1988,10 @@ static inline void idle_task_exit(void)

    #if defined(CONFIG_NO_HZ) && defined(CONFIG_SMP)
    extern void wake_up_idle_cpu(int cpu);
    +extern int sched_needs_cpu(int cpu);
    #else
    static inline void wake_up_idle_cpu(int cpu) { }
    +static inline void sched_needs_cpu(int cpu) { }
    #endif

    extern unsigned int sysctl_sched_latency;
    Index: linux-3.0-tip/kernel/sched/core.c
    ===================================================================
    --- linux-3.0-tip.orig/kernel/sched/core.c
    +++ linux-3.0-tip/kernel/sched/core.c
    @@ -587,6 +587,13 @@ static inline bool got_nohz_idle_kick(vo
    return idle_cpu(smp_processor_id()) && this_rq()->nohz_balance_kick;
    }

    +#ifdef CONFIG_SMP
    +int sched_needs_cpu(int cpu)
    +{
    + return cpu_rq(cpu)->avg_event < sysctl_sched_migration_cost;
    +}
    +#endif
    +
    #else /* CONFIG_NO_HZ */

    static inline bool got_nohz_idle_kick(void)
    Index: linux-3.0-tip/kernel/time/tick-sched.c
    ===================================================================
    --- linux-3.0-tip.orig/kernel/time/tick-sched.c
    +++ linux-3.0-tip/kernel/time/tick-sched.c
    @@ -352,7 +352,7 @@ void tick_nohz_stop_sched_tick(int inidl
    } while (read_seqretry(&xtime_lock, seq));

    if (rcu_needs_cpu(cpu) || printk_needs_cpu(cpu) ||
    - arch_needs_cpu(cpu)) {
    + arch_needs_cpu(cpu) || sched_needs_cpu(cpu)) {
    next_jiffies = last_jiffies + 1;
    delta_jiffies = 1;
    } else {



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